1. Field of the Invention
The present invention relates to a magnetic tape cassette and more particularly to a magnetic tape cassette having means for preventing tape displacement on the reels in the direction of the width of the tape.
2. Description of the Prior Art
Recently, it has been proposed to provide miniaturized light-weight cassette tape recorders and miniaturized magnetic tape cassettes for use therewith. Further, it is highly desirable to provide such magnetic tape received within the cassette of this type having high density recording and reproduction for a long period of time. In order to satisfy the latter requirements, tapes such as the so-called C-120, C-180 tapes have been designed. Moreover, to achieve high density recording, the surface of the recording medium must be treated so as to have a mirror face finish.
In a well-known guide mechanism for guiding a cassette tape, such as is shown in FIG. 1, if the coefficient of sliding friction between layers of a recording surface of tape and a backing material is large, such as more than 0.4, or if a layer of air is between the tape layers and cannot be removed, the tape becomes curled up dishwise or stepwise, causing the tape to loop or jam as well as becoming deformed, and in the worst case, causing a stop of tape travel. This tendency is more marked as the speed of the tape increases at which tape is quickly fed or unreeled.
As shown in FIG. 1, a well-known tape travel guide mechanism for a cassette tape comprises a pair of reels 2 and 3 encased in a hollow case 1 formed by fixing an upper case 1a and a lower case 1b by means of fixing members 1c. The cassette includes a fixed guide pin 4, a rotary guide roller 5, a pressing pad 6, a rotary guide roller 7, a fixed guide pin 8, and flat guide plates 9 (only one shown in FIG. 1) disposed between the inner sides of said upper case 1a and lower case 1b and the opposite sides of said reels 2 and 3.
Tape T, wound on the reel 2, is fed to the reel 3 orderly passing through the fixed guide pin 4, rotary guide roller 5, pressing pad 6 for urging tape T against a recording and reproducing head, rotary guide roller 7, and fixed guide pin 8, in such a manner that the opposite edges of the tape are guided by the respective guide plates 9 without being greatly displaced in the width direction of the tape.
However, the prior art cassette poses a drawback such that when the tape quickly wound in one direction and then the other direction, the edge portions of the tape on the reel 2 or 3 are greatly displaced in the width direction so that the edges strongly hit almost the entire area of the inner wall surface of the guide plate 9 thereby increasing the feed-out back tension magnitude by two or three times. As a consequence breakage or creases, which remain as a permanent strain, tend to occur near the edges and a signal recorded on the edge track becomes abnormal, rendering faithful reproduction impossible.